- Email: [email protected]
The specific heat of aluminium
Chemical Sectzon.
Feb.,I892. ]
121
Tt~; S P E C I F I C H E A T OF A L U M I N I U M . BY J. w .
RICHARDS, L e h i g h U n i v e r s i t y .
[Read at the s/a[ed mee/ing of the Chemz'cal 5"ec[ion, heht D~'cembcr I5, IS9L ]
T h e d e t e r m i n a t i o n s of the specific h e a t of a l u m i n i u m are b u t few in n u m b e r , and y e t v a r y widely. As soon as Sainte-Claire Deville h a d o b t a i n e d a b u t t o n of a l u m i n i u m , in 1855, his friend R e g n a u l t i m p o r t u n e d h i m for a specimen w i t h w h i c h to d e t e r m i n e its specific heat, and a l t h o u g h Deville knew t h a t the m e t a l he h a d m a d e was far from pure, y e t he yielded to R e g n a u l t ' s request and f u r n i s h e d h i m w i t h three small pieces, w h i c h a n a l y z e d : Silicon, . Iron, . . Copper, . Lead, . . . Aluminium
. . . . . . . . . .
. . . . . . . . . .
. . . . . . . . . .
. . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .
. . . . .
. . . . .
. . . . .
~'87 2'4o 6'38 traces 88'35
R e g n a n l t d e t e r m i n e d t h e m e a n specific h e a t of this m e t a l b e t w e e n 25 ° and 97 ° to be o'2056. He a t t e m p t e d to calculate a p p r o x i m a t e l y the specific h e a t of pure a l u m i n i u m by a l l o w i n g for the i m p u r i t i e s present. In d o i n g this he a s s u m e d the specific h e a t of silicon to be o'x425, it not h a v i n g been t h e n d e t e r m i n e d , and his calculation gave him o'218I as the n u m b e r for pure a l u m i n i u m . H a d he, however, used w h a t we now k n o w to be the specific h e a t of silicon, o"2I, he would have calculated 0"220o as the specific h e a t of pure a l u m i n i u m b e t w e e n 25 ° and 97 °. A y e a r later R e g n a u l t o b t a i n e d a l u m i n i u m about 97 per cent. pure. H e o b t a i n e d for this, b e t w e e n I4 ° and 97 ° , o'2122. Allowing for the i m p u r i t i e s present, he calculated o'2143 as the probable n u m b e r for pure a l u m i n i u m . It m a y be r e m a r k e d in passing, as a curious fact, t h a t R e g n a u l t t r e a t s these m e a n values as if t h e y were invariable constants, i n d e p e n d e n t of the r a n g e of t e m p e r a t u r e t h r o u g h w h i c h t h e y were d e t e r m i n e d . F o l l o w i n g R e g n a u l t came Kopp, who in I863 m a d e d e t e r m i n a t i o n s w i t h o r d i n a r y Parisian a l u m i n i u m . He
122
[J. F. I.,
C h e m i c a l Section.
o b t a i n e d o'2oeo as t h e m e a n v a l u e b e t w e e n 2o ° a n d 52 °. H o w e v e r , no a n a l y s i s is g i v e n of t h e m e t a l u s e d , a n d f r o m a c o n s i d e r a t i o n of t h e w a y in w h i c h K o p p e x p e r i m e n t e d , a n d t h e d e g r e e of a c c u r a c y w h i c h w a s p o s s i b l e in his e x p e r i m e n t s , it is e v i d e n t t h a t his r e s u l t s are of v e r y l i t t l e value. F o r i n s t a n c e , f o u r d e t e r m i n a t i o n s g a v e h i m o' ! 97 ° 0"2C00
0"2070 0"2020
f r o m w h i c h h e s i m p l y d e d u c e s 0"2020 as a n a v e r a g e v a l u e . In I882, Professor Mallet m a d e some a b s o l u t e l y p u r e a l u m i n i u m for his r e s e a r c h e s on t h e a t o m i c w e i g h t , a n d h e d e t e r m i n e d its m e a n specific h e a t b e t w e e n 0 ° a n d Ioo °, b y m e a n s of a B u n s e n ice c a l o r i m e t e r , to b e 0"2253. S i n c e n o i m p u r i t y w a s p r e s e n t in t h e m e t a l , t h i s d e t e r m i n a t i o n is free f r o m o n e of t h e s o u r c e s of e r r o r of t h e p r e v i o u s ones.
More recently, Naccari, the noted Italian physicist, states t h a t h e o b t a i n s for t h e t r u e specific h e a t of a l u m i n i u m a t various temperatures the following values : I go O'2135
5 °0 O"2164
I OO°
200 °
3OO°
O"221 !
0"2306
O"24OI
I t will b e n o t i c e d t h a t t h e s e v a l u e s i n d i c a t e t h a t t h e specific h e a t i n c r e a s e s 0"0095 p e r ~oo °, a n d l e a d to t h e formulae : s = o'2ti6 q- -oooo95 ! Sm = o'21,6 ~ "oooo475(l, ~- f,,) in w h i c h o ' 2 I I 6 is t h e t r u e specific h e a t a t o °. T h e m e a n b e t w e e n o ° a n d Ioo ° w o u l d b e o'2164, c o m p a r i n g well w i t h R e g n a u l t ' s r e s u l t s , b u t m u c h l o w e r t h a n Mallet's. I t is not s t a t e d w h a t w a s t h e p u r i t y of t h e m e t a l u s e d b y N a c c a r i . T h e q u e s t i o n w h i c h t h e w r i t e r set o u t to s o l v e p r e s e n t e d itself to h i m in t h i s w a y : W h o is n e a r e s t t h e t r u t h , R e g n a u l t a n d N a c c a r i , or M a l l e t ? I o b t a i n e d s o m e a l u m i n i u m m a d e b y t h e H a l l process, which analyzed : Silicon, . . . . . . . . . . . . . . . . . . . . . . . . . oo7 Iron, . . . . . . . . . . . . . . . . . . . . . . . . . . trace Aluminium, • . . . . . . . . . . . . . . . . . . . . . 99"93,
Feb., ~89.~.]
C/~emical $cctian.
12 3
Since the a t o m i c w e i g h t of silicon is a l m o s t i dent i cal w i t h t h a t of a l u m i n i u m , it was felt safe to n e g l e c t t h e influence of th e 0"o7 per cent. p r e s e n t . T h r e e m e t h o d s of p r o c e d u r e were used. First, a l arge w e i g h t of a l u m i n i u m ( t oo- 2oo grins.) was p u t into an e m p t y calo r im e t e r , w h o s e w a t e r e q u i v a l e n t h a d b e e n a e e u r a t e l v d e t e r m i n e d b y e x p e r i m e n t , and allowed to s t a n d several hours. W h e n t he t e m p e r a t u r e was n e a r l y const ant , a k n o wn w e i g h t of w a t e r at a h i g h e r t e m p e r a t u r e was run in, and t h e total loss of h e a t c a l c u l a t e d f r o m t h e o b s e r v a t i o n s . T h i s m e t h o d g a v e m e a n specific h e a t s b e t w e e n a b o u t I6 ° and 22 °. Secondly, t he a l u m i n i u m was s u s p e n d e d in s t e a m and d r o p p e d i n t o t he w a t e r in a cal ori m et er. T h i s g a v e values f r o m 2o ° to ~oo °. T h i r d l y , two e x a c t l y similar c a l o r i m e t e r s w e r e used. • T h e a l u m i n i u m and a p l a t i n u m ball w e i g h i n g fifty-two g r a m m e s w ere placed on a p l a t i n u m s u p p o r t and h e a t e d t o g e t h e r e i t h e r in an air bat.h to IZO°, or in a small f u r n a c e up to 4oo °, 5oo ° and 6oo °. T h e platin u m ball was d r o p p e d into one c a l o r i m e t e r and t he l u m p of a l u m i n i u m i nt o a n o t h e r . F r o m t h e h e a t g i v e n o~It b y t h e p l a t i n u m its t e m p e r a t u r e was calculated, a n d a s s u m i n g t h a t th e a l u m i n i u m h a d b e e n at t he s a m e t e m p e r a t u r e , I had t h e d a t a for c a l c u l a t i n g its m e a n specific heat. T h e t h i r d m e t h o d g a v e t he m o s t c o n c o r d a n t results. T h e first m e t h o d was used for such a small r a n g e of t e m p e r a t u r e t h a t t he e x p e r i m e n t a l e r r o r s w e r e large. T h e second m e t h o d was d e f e c t i v e in d e f a u l t of s u i t a b l e a p p a r a t u s to s ecu r e t h e i n s t a n t t r a n s f e r of t he m e t a l f r o m t h e s t e a m into th e c a l o r i m e t e r . T h e t hi r d m e t h o d had the a d v a n t a g e , t h a t since t h e p l a t i n u m and a l u m i n i u m w ere t a k e n out of the f u r n a c e t o g e t h e r and w e r e d r o p p e d a l m o s t s i m u l t a n e ously into the c a l o r i m e t e r s , it could fairly be a s s u m e d t h a t t h e y w o u l d cool a b o u t the s a m e a m o u n t in t he two or t h r e e seconds d u r i n g w hi c h t h e y were e x p o s e d to t he air. T h e w r i t e r has m a d e two e x p e r i m e n t s b y the first m e t h o d , five b y t he second and si xt een b y t he third. S e l e e t i n g t h o s e e x p e r i m e n t s , w hi ch w ere e x p e r i m e n t a l l y t he n e a r e s t to p e r f e c t ones, and c o r r e l a t i n g t h e dat a by t h e
Chemwal Section.
~2 4
m e t h o d of l e a s t arrived at :
squares,
Sm = 0"2220 S = 0"2220
the
[J. F. I.,
following
+ 0"00005 + 0"0001
formulae
were
(tl + t~) t
i n w h i c h 0"2220 is t h e t r u e s p e c i f i c h e a t a t 0 ° C. F r o m t h e s e f o r m u l a e t h e f o l l o w i n g v a l u e s will ibe s h o w n : Temperature.
True Specific Heat.
O°
0"2220
20 ° i0o °
Mean Specific Heat.
Range of Temperature. G° ~
0"2270
IOO °
0"2240 0"2320
oo m 625° (melting point) 625 °
0.2533
0"2845
(melting point) Total caloric capacity to the melting point,
f
. . 158"3
I t is s e e n t h a t t h e a u t h o r ' s r e s u l t s c o n f i r m M a l l e t ' s , d e t e r m i n a t i o n , as f a r as t h e t r u e s p e c i f i c h e a t is c o n c e r n e d , a n d a g r e e c l o s e l y w i t h N a c c a r i ' s o b s e r v a t i o n of i t s r a t e of increase with the temperature.
Feb.,I892. ]
121
Tt~; S P E C I F I C H E A T OF A L U M I N I U M . BY J. w .
RICHARDS, L e h i g h U n i v e r s i t y .
[Read at the s/a[ed mee/ing of the Chemz'cal 5"ec[ion, heht D~'cembcr I5, IS9L ]
T h e d e t e r m i n a t i o n s of the specific h e a t of a l u m i n i u m are b u t few in n u m b e r , and y e t v a r y widely. As soon as Sainte-Claire Deville h a d o b t a i n e d a b u t t o n of a l u m i n i u m , in 1855, his friend R e g n a u l t i m p o r t u n e d h i m for a specimen w i t h w h i c h to d e t e r m i n e its specific heat, and a l t h o u g h Deville knew t h a t the m e t a l he h a d m a d e was far from pure, y e t he yielded to R e g n a u l t ' s request and f u r n i s h e d h i m w i t h three small pieces, w h i c h a n a l y z e d : Silicon, . Iron, . . Copper, . Lead, . . . Aluminium
. . . . . . . . . .
. . . . . . . . . .
. . . . . . . . . .
. . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .
. . . . .
. . . . .
. . . . .
~'87 2'4o 6'38 traces 88'35
R e g n a n l t d e t e r m i n e d t h e m e a n specific h e a t of this m e t a l b e t w e e n 25 ° and 97 ° to be o'2056. He a t t e m p t e d to calculate a p p r o x i m a t e l y the specific h e a t of pure a l u m i n i u m by a l l o w i n g for the i m p u r i t i e s present. In d o i n g this he a s s u m e d the specific h e a t of silicon to be o'x425, it not h a v i n g been t h e n d e t e r m i n e d , and his calculation gave him o'218I as the n u m b e r for pure a l u m i n i u m . H a d he, however, used w h a t we now k n o w to be the specific h e a t of silicon, o"2I, he would have calculated 0"220o as the specific h e a t of pure a l u m i n i u m b e t w e e n 25 ° and 97 °. A y e a r later R e g n a u l t o b t a i n e d a l u m i n i u m about 97 per cent. pure. H e o b t a i n e d for this, b e t w e e n I4 ° and 97 ° , o'2122. Allowing for the i m p u r i t i e s present, he calculated o'2143 as the probable n u m b e r for pure a l u m i n i u m . It m a y be r e m a r k e d in passing, as a curious fact, t h a t R e g n a u l t t r e a t s these m e a n values as if t h e y were invariable constants, i n d e p e n d e n t of the r a n g e of t e m p e r a t u r e t h r o u g h w h i c h t h e y were d e t e r m i n e d . F o l l o w i n g R e g n a u l t came Kopp, who in I863 m a d e d e t e r m i n a t i o n s w i t h o r d i n a r y Parisian a l u m i n i u m . He
122
[J. F. I.,
C h e m i c a l Section.
o b t a i n e d o'2oeo as t h e m e a n v a l u e b e t w e e n 2o ° a n d 52 °. H o w e v e r , no a n a l y s i s is g i v e n of t h e m e t a l u s e d , a n d f r o m a c o n s i d e r a t i o n of t h e w a y in w h i c h K o p p e x p e r i m e n t e d , a n d t h e d e g r e e of a c c u r a c y w h i c h w a s p o s s i b l e in his e x p e r i m e n t s , it is e v i d e n t t h a t his r e s u l t s are of v e r y l i t t l e value. F o r i n s t a n c e , f o u r d e t e r m i n a t i o n s g a v e h i m o' ! 97 ° 0"2C00
0"2070 0"2020
f r o m w h i c h h e s i m p l y d e d u c e s 0"2020 as a n a v e r a g e v a l u e . In I882, Professor Mallet m a d e some a b s o l u t e l y p u r e a l u m i n i u m for his r e s e a r c h e s on t h e a t o m i c w e i g h t , a n d h e d e t e r m i n e d its m e a n specific h e a t b e t w e e n 0 ° a n d Ioo °, b y m e a n s of a B u n s e n ice c a l o r i m e t e r , to b e 0"2253. S i n c e n o i m p u r i t y w a s p r e s e n t in t h e m e t a l , t h i s d e t e r m i n a t i o n is free f r o m o n e of t h e s o u r c e s of e r r o r of t h e p r e v i o u s ones.
More recently, Naccari, the noted Italian physicist, states t h a t h e o b t a i n s for t h e t r u e specific h e a t of a l u m i n i u m a t various temperatures the following values : I go O'2135
5 °0 O"2164
I OO°
200 °
3OO°
O"221 !
0"2306
O"24OI
I t will b e n o t i c e d t h a t t h e s e v a l u e s i n d i c a t e t h a t t h e specific h e a t i n c r e a s e s 0"0095 p e r ~oo °, a n d l e a d to t h e formulae : s = o'2ti6 q- -oooo95 ! Sm = o'21,6 ~ "oooo475(l, ~- f,,) in w h i c h o ' 2 I I 6 is t h e t r u e specific h e a t a t o °. T h e m e a n b e t w e e n o ° a n d Ioo ° w o u l d b e o'2164, c o m p a r i n g well w i t h R e g n a u l t ' s r e s u l t s , b u t m u c h l o w e r t h a n Mallet's. I t is not s t a t e d w h a t w a s t h e p u r i t y of t h e m e t a l u s e d b y N a c c a r i . T h e q u e s t i o n w h i c h t h e w r i t e r set o u t to s o l v e p r e s e n t e d itself to h i m in t h i s w a y : W h o is n e a r e s t t h e t r u t h , R e g n a u l t a n d N a c c a r i , or M a l l e t ? I o b t a i n e d s o m e a l u m i n i u m m a d e b y t h e H a l l process, which analyzed : Silicon, . . . . . . . . . . . . . . . . . . . . . . . . . oo7 Iron, . . . . . . . . . . . . . . . . . . . . . . . . . . trace Aluminium, • . . . . . . . . . . . . . . . . . . . . . 99"93,
Feb., ~89.~.]
C/~emical $cctian.
12 3
Since the a t o m i c w e i g h t of silicon is a l m o s t i dent i cal w i t h t h a t of a l u m i n i u m , it was felt safe to n e g l e c t t h e influence of th e 0"o7 per cent. p r e s e n t . T h r e e m e t h o d s of p r o c e d u r e were used. First, a l arge w e i g h t of a l u m i n i u m ( t oo- 2oo grins.) was p u t into an e m p t y calo r im e t e r , w h o s e w a t e r e q u i v a l e n t h a d b e e n a e e u r a t e l v d e t e r m i n e d b y e x p e r i m e n t , and allowed to s t a n d several hours. W h e n t he t e m p e r a t u r e was n e a r l y const ant , a k n o wn w e i g h t of w a t e r at a h i g h e r t e m p e r a t u r e was run in, and t h e total loss of h e a t c a l c u l a t e d f r o m t h e o b s e r v a t i o n s . T h i s m e t h o d g a v e m e a n specific h e a t s b e t w e e n a b o u t I6 ° and 22 °. Secondly, t he a l u m i n i u m was s u s p e n d e d in s t e a m and d r o p p e d i n t o t he w a t e r in a cal ori m et er. T h i s g a v e values f r o m 2o ° to ~oo °. T h i r d l y , two e x a c t l y similar c a l o r i m e t e r s w e r e used. • T h e a l u m i n i u m and a p l a t i n u m ball w e i g h i n g fifty-two g r a m m e s w ere placed on a p l a t i n u m s u p p o r t and h e a t e d t o g e t h e r e i t h e r in an air bat.h to IZO°, or in a small f u r n a c e up to 4oo °, 5oo ° and 6oo °. T h e platin u m ball was d r o p p e d into one c a l o r i m e t e r and t he l u m p of a l u m i n i u m i nt o a n o t h e r . F r o m t h e h e a t g i v e n o~It b y t h e p l a t i n u m its t e m p e r a t u r e was calculated, a n d a s s u m i n g t h a t th e a l u m i n i u m h a d b e e n at t he s a m e t e m p e r a t u r e , I had t h e d a t a for c a l c u l a t i n g its m e a n specific heat. T h e t h i r d m e t h o d g a v e t he m o s t c o n c o r d a n t results. T h e first m e t h o d was used for such a small r a n g e of t e m p e r a t u r e t h a t t he e x p e r i m e n t a l e r r o r s w e r e large. T h e second m e t h o d was d e f e c t i v e in d e f a u l t of s u i t a b l e a p p a r a t u s to s ecu r e t h e i n s t a n t t r a n s f e r of t he m e t a l f r o m t h e s t e a m into th e c a l o r i m e t e r . T h e t hi r d m e t h o d had the a d v a n t a g e , t h a t since t h e p l a t i n u m and a l u m i n i u m w ere t a k e n out of the f u r n a c e t o g e t h e r and w e r e d r o p p e d a l m o s t s i m u l t a n e ously into the c a l o r i m e t e r s , it could fairly be a s s u m e d t h a t t h e y w o u l d cool a b o u t the s a m e a m o u n t in t he two or t h r e e seconds d u r i n g w hi c h t h e y were e x p o s e d to t he air. T h e w r i t e r has m a d e two e x p e r i m e n t s b y the first m e t h o d , five b y t he second and si xt een b y t he third. S e l e e t i n g t h o s e e x p e r i m e n t s , w hi ch w ere e x p e r i m e n t a l l y t he n e a r e s t to p e r f e c t ones, and c o r r e l a t i n g t h e dat a by t h e
Chemwal Section.
~2 4
m e t h o d of l e a s t arrived at :
squares,
Sm = 0"2220 S = 0"2220
the
[J. F. I.,
following
+ 0"00005 + 0"0001
formulae
were
(tl + t~) t
i n w h i c h 0"2220 is t h e t r u e s p e c i f i c h e a t a t 0 ° C. F r o m t h e s e f o r m u l a e t h e f o l l o w i n g v a l u e s will ibe s h o w n : Temperature.
True Specific Heat.
O°
0"2220
20 ° i0o °
Mean Specific Heat.
Range of Temperature. G° ~
0"2270
IOO °
0"2240 0"2320
oo m 625° (melting point) 625 °
0.2533
0"2845
(melting point) Total caloric capacity to the melting point,
f
. . 158"3
I t is s e e n t h a t t h e a u t h o r ' s r e s u l t s c o n f i r m M a l l e t ' s , d e t e r m i n a t i o n , as f a r as t h e t r u e s p e c i f i c h e a t is c o n c e r n e d , a n d a g r e e c l o s e l y w i t h N a c c a r i ' s o b s e r v a t i o n of i t s r a t e of increase with the temperature.